Peel the potatoes and cook them in a generous amount of water. Leave them almost half cooked. Then and with the help of a spoon, make a hole in each potato so you can afterwards fill it in with the following.
Add the 3 Tbsp of oil to the pan and then fry the minced porkloin, together with the deseeded and peeled tomato and the chopped onion. Pour it through a sieve to get out the remaining oil.
Preheat oven at 180º. Place the mixture in every potato and then sprinkle over with cheese.
Place potatoes in tray and place tray in oven until cheese melts. Then put them to gratiné.